Meta-analysis found that studies may have overestimated Caesarean section risks for attention-deficit hyperactivity disorder by ignoring confounding factors.

AIM: Epidemiological studies on associations between Caesarean sections (C-sections) and attention-deficit hyperactivity disorder (ADHD) have been inconsistent, and we performed a meta-analysis. METHODS: We systematically searched PubMed and Embase to December 2018 and included nine hospital-based and population registry studies published in 2011-2018. These covered a total study cohort of more than 2.5 million people in eight countries: Australia, Brazil, Denmark, Finland, Germany, Sweden, Turkey and the UK. The analysis provided summary odds ratios (ORs) and 95% confidence intervals (CI) while taking heterogeneity into account. RESULTS: We found that that C-sections were associated with a small increase in the risk of ADHD (OR 1.14, 95% CI 1.11, 1.17, I2 0%) in offspring. In subgroup analyses, the association remained for both infants born after elective C-sections (OR, 1.15, 1.11, 1.19, I2 0%) and emergency C-sections (OR, 1.13, 1.1, 1.17, I2 45.4%). However, these were only marginally significant when we pooled data from siblings from other pregnancies (OR, 1.06, 1.00-1.13, I2 0%), implying that the association was due to confounding. CONCLUSION: The statistically significant association between C-sections and ADHD in children can be partially explained by unmeasured confounding. Further research controlling for important confounders is required before firm conclusions can be drawn.

Infection, antibiotic exposure, and risk of celiac disease: A systematic review and meta-analysis.

BACKGROUND AND AIM: There is evidence of a relationship between infection (and the associated antibiotic exposure) and the risk of celiac disease (CD). This study performed a meta-analysis to investigate this relationship. METHODS: To identify relevant studies, we conducted systematic searches of the PubMed, Embase, and Cochrane databases for articles published up to April 2019. Random effects models were used to determine overall pooled estimates and 95% confidence intervals (CIs). RESULTS: The meta-analysis included 19 observational studies (15 on infection and six on antibiotic exposure). Our results showed that any infection was associated with an increased risk of CD later in life (odds ratio, 1.37; 95% CI: 1.2-1.56; P < 0.001). The I2 was 94% (high heterogeneity among studies). Subgroup analyses suggested that the risk of CD is not affected by the type of infectious agent, timing of exposure, and site of infection. Exposure to antibiotics was also associated with new-onset CD (odds ratio, 1.2; 95% CI: 1.04-1.39; P < 0.001). CONCLUSION: Exposure to early infection or antibiotic appears to increase the odds of developing CD, suggesting that intestinal immune or microbiota dysbiosis may play a role in the pathogenesis of CD. These findings may influence clinical management and primary prevention of CD. However, noncausal explanations for these positive associations cannot be excluded.